Burner control apparatus with component checking means



Jan. 27,1953 J. M WILSON 2,626,657

BURNER CONTROL APPARATUS WITH COMPONENT CHECKING MEANS Filed June 27,1949 2 SHEETS-SHEET l ll 3nventor b 1 I 1 I I JOHN M.W|LSON (IttornegPatented Jan. 27, 1953 UNITED STATES PATENT OFFICE BURNER CONTROLAPPARATUS WITH COMIONENT'CHECKING MEANS Application June 27, 1949,Serial No. 101,507

18 Claims. 1

The present invention relates to burner control apparatus andparticularly to that type of burner control apparatus employingcondenser timing for obtaining safety shutdown and proper sequencing ofthe burner control. This application is a continuation in part of anapplication filed by the present inventor for Burner Control Apparatus,on March 10, 1948, Serial No. 13,981, now abandoned.

In some present day burner installations, particularly those employinggas as a fuel, it is desirable to have almost immediate shutdown in theevent, that upon initiation of operation, combustion is not establishedor upon the occurrence of a flame failure. This may be accomplished byusin an electronic flame detector 'to regulate the charging time of acondenser through resistor. When the condenser is charged suffi'ciently,the charge may be used to bias an electron discharge device out ofconduction to render the apparatus inoperative. When combustion isdetected by the electronic flame detector the charging circuit of thecondenser is rendered ineffective.

By using an electronic flame detector in the present invention it ispossible to shut the burner down the instant it is determined combustionis not present. The electronic flame detector that has been employedresponds almost instantly to the presence or absence of flame. As theflame detector employs an electron discharge devic which is subject tofailure, it is necessary to provide a control apparatus which will bequickly rendered inoperative upon the flame failure and which will checkthe circuit components in the event that the flame detector should beinoperative or should be operating falsely.

It is therefore an object of th present invention to provide a burnercontrol apparatus of the electronic type which will quickly respond tothe presence or absence of flame and which will be maintainedinoperative in the event there is a component failure in the controlapparatus.

Another object of the present invention is to provide a burner controlapparatus which employs resistor-condenser timing to accomplish shutdownof a burner when there is a flame failure and which checks thecomponents of the control apparatus to maintain the burner inoperativewhen there is a false indication of flame.

Still another object of the present invention is to provide a controlapparatus employing an electron discharge device which is renderedoperative upon the need for operation of a burner and inoperative uponthe occurrenc of a flame failure by a biasing voltage charging acondenser associated with the discharge device and further biasing thedischarge device to be maintained inoperative when a flame detectiondevice falsely indicates flame.

A further object of the present invention is to provide a burner controlapparatus employing an electron discharg device which is renderedoperative upon the need for operation of a burner and an electronicflame detector which will render the discharge device inoperative whenthere is a flame failure and maintain the discharge device inoperativewhen there is a false indication of flame.

A still further object of the present invention is to provide a burnercontrol apparatus employing an electron discharge device which is biasedto be inoperative upon a flame failure by one biasing circuit and to bebiased to be inoperative by a second circuit when there is a falseindication of flame and where the latter biasing circuit will bemaintained continuously until the fault causin the false indication offlame is removed.

These and other more detailed and specific objects will be disclosed inthe course of the following specification, reference being had to theaccompanying drawings of which:

Figure 1 shows in detail one embodiment of the invention as applied to agas burner control. and

Figure 2 shows the invention in slightly modifled form.

Referring to Figure 1, the numeral Ill represents a gas burner which isadapted to be supplied fuel through a conduit II. Controlling the flowof fuel through the conduit 1 l is a valve [2 which is electricallyoperated. The fuel of the burner is ignited by a pair of ignitionelectrodes l3 and 14 which are operatively energized by an ignitiontransformer i5 consisting of a primary winding 16, energized from acommon source of power, and a secondary winding H. An electric sparkbetween the ignition electrodes will ignite the gas flowing from a pilotnozzle l8. Supplying fuel to the pilot nozzle [8 is a conduit I9 whichhas controlling the flow of fuel therein, a further electricallyoperated valve 20. Both valves l2 and 20 are of the type which aremaintained open as long as energized and moved to closed position upondeenergization.

To indicate the need for operation of the burner ID, a thermostat 2| hasbeen provided which may be seen to consist of a bimetal 22 which isoperable upon the temperature falling and rising to move a switch blade23 into and out of engagement respectively ith an associated switchcontact 24. Located within a housing 3?, indicated by dotted lines, arethe control circuits for actuating the valves I2 and 20 and ignitiontransformer I5 upon the demand for heat as indicated by thermostat 2I.Energized by the actuation of the thermostat 2| is a control relay I20having a relay winding I2I which is operable when energized to move anassociated switch blade I22 from engagement with a switch contact I23into engagement with a further contact I24. Energized by the controlrelay I2!) is a main control electron discharge device 25 in the form ofa triode having an anode 25, a control electrode 21, and a cathode 28.Energized by the current flow through the triode 25 is a relay 29 whichmay be seen to consist of a relay winding 3!], adapted to move a pair ofswitch blades El and 32 which are normally biased so that the switchblade'3l engages a contact 33 and the switch blade 32 'is biased out ofengagement with the contact 34. When relay 3a is energized, the switchblades 3| and 32 engage contacts 35 and 34 respectively. A condenser 36is connected across the relay winding 38 to function in a normal mannerto by-pass th alternating current flowing in the energizing circuit fortriode 25.

Energized by the transformer '45 is an electron discharge device 50 inthe formof a triode having an anode 5|, a control electrode 52, and acathode 53. Also energized by the transformer 45 is a further electrondischarge device 54 in the "form of a triode having an anode 55, acontrol electrode 56, and a cathode 51. Associated with the inputoftriode 50 is a biasing condenser 58,

"a filter network consisting of a resistor 59 and condenser 60, and abiasing resistor 6I.

Associated with the input of triode 54 are a pair of resistors 62 and63. The output circuit of the triode 54 includes a relay 65 having arelay winding 66 which is adapted to move a pair of switch blades 61 and68. The switch blades 61 and 68 are normally biased so that the switchblade 67 engages a switch contact 69 and the switch blade '68 is biasedout of engagement with an associated contact Ill. When the relay isenergized the switch blade 61 moves into engagement with an associatedcontact ll and the switch blade 63 moves into engagement with theassociated contact Ill. A condenser I2 is provided to by-pass thealternating current around the relay winding 66. Also associated withthe flame detectionportion of the control apparatus is an electrode I5which is positioned ina manner to intersect the flame from either thepilot nozzle I8 or the burner Ill.

Normal operation of Figure 1 In considering the normal operation of thesubject control'apparatus it will be assumed that control relays I20and-Minor the'flame detection relay are energized. Under theseconditions the ignition transformer will not be energized, the pilotvalve 26 will not be energized and the main control valve I2 will not beenergized. The thermostat 2I is used to indicate the need for operationof the burner It and upon such need the bimetal 22 will move the switchblade 23 into engagement with its associated contact 24. With blade 23engaging switch contact 24 an energizing circuit is completed to thecontrol relay I20 from the input power line Bil through conductors 8|and 82, contact 24, blade 23, bimetal 22, conductor 33, relay windingI2I, and conductors and ill to the other input power line 88. When thisrelay becomes energized, the switch blade I22 will move into engagementwith contact I24 to complete an energizing circuit to the main controltriode 2 5. This circuit to triode 25 may be traced from the input powerline 88 through conductors B7, 85, and 84, relay winding '30, anode 26,cathode 28, conductor I25, switch blade I22, switch contact I24, andconductors I26 and 8 I back to the other input power line 86. It will benoted that this last traced circuit includes the relay winding 39. Inthe absence of any biasing voltage on the input of the triode 25 theresultant current flow will cause relay winding 30 to move the switchblades 3| and 32 into engagement with their associated switch contacts35 and 3d respectively.

When switch blade 32 engages switch contact 35. an energizing circuit iscompleted to the ignition transformer is and the pilot valve 26. Thiscircuit may be traced from the input power line '88 through conductors8?, 85 and 85, switch blade 32, switch contact '34, conductors 90 and 9I, switch blade 5?, switch contact 69, conductor 92, ignitiontransformer primary winding I6, and conductors 93 and 9 back to theother input power line 80. The energizing circuit to the pilot valve 20is almost identical to the last traced circuit except relay I55 and thiscircuit may be traced from the that it does not include switch contactsof the input power line 88 through conductors 81, B5 and 89, switchcontact 32, switch contact 34, conductors 9B and 95, pilot valve 26, andconductors S3 and'S i to the other input power line 813. With pilotvalve 20 and ignition transformer I5 energized, fuel will pass throughthe conduit I9 to the pilot nozzle I8 where the spark across theignition electrodes I3 and 54 will ignite the fuel.

The flame detector employed in the subject control apparatus is of thetype that is adapted to utilize the rectifying characteristics of aflame bridging a pair of flame electrodes. It is a well known phenomenonthat when a pair 0': flame electrodes are positioned in the path of aflame and voltage is applied to those electrodes there will be a currentflow through the flame. The current flow through the flame will begreater in one direction than it is in the other, the direction ofgreatest electron conductivity being in the direction of propagation ofthe flame. Just how this is utilized in the present control apparatuswill be understood from the discussion of the flame detector whichfollows.

The flame electrode circuit is used to bias triode 50 into and out ofconduction in accordance with the presence or absence of flame that maybe existing between the pilot nozzle I 8 and the flame electrode ?5. Theflame detection circuit may be traced from the lower terminal orsecondary 41 through conductors I0! and Itil, ground 99 ground 98, pilotnozzle i8, electrode 15, conductor -9'i,-condenser"58 and conductor 95to the tap 48 5 of the secondary 41. As there'is alternating current onthe secondary 4! there will be alternating current applied across thegap between the flame electrode I5 and the pilot nozzle I8 which willmean that there will be a unidirectional component of current flowthrough the last traced circuit which will tend to charge the condenser58 to a predetermined voltage of a polarity which will be negative onthe lower terminal and positive on the upper terminal. The condenser 58will be so charged during the half cycle of the alternating power supplywhen the tap 48 is positive with respect to the lower terminal ofsecondary 41. On the following half cycle, the condenser 58 willdischarge in a circuit that may be traced from the lower terminal ofcondenser 58 through resistors 59 and GI, conductor I01, secondary 41,tap 48 and conductor 96 to the upper terminal of condenser 58. Thecurrent flow through resistor BI will result in condenser 60 assuming acharge which will be negative on the upper terminal and positive on thelower terminal. The resistor 59 and the condenser 60 form a filternetwork which serves to smooth out any flame fluctuation occurring atthe flame electrode I5 and changes in the charging rate of condenser 58.With condenser 89 being effectively charged by the charge on thecondenser'58 the triode 50 will be biased to be nonconductive since thecondenser 60 is connected directly between the control electrode 52 andthe cathode 53. When triode 50 is nonconducting the triode 54 will bebiased into conduction and will energize relay 85 in a manner to beexplained hereinafter. The energizing circuit for the triode 54 may betraced from the upper terminal of the secondary 41 through conductorI06, relay winding 68, conductor I07, anode 55, cathode 51, andconductors I08, I03 and I02, back to the tap 48 of the secondary 41. Thetriode 54 will be conducting since the control electrode 56 is connectedto a voltage divider consisting of resistors 62 and 63 connected acrossthe upper half of the secondary 47, and is biased to be conductive sincethe control electrode will be positive with respect to the cathode onthe conducting half cycle of the power source.

When the relay 85 becomes energized the relay winding 88 will move theswitch blades BTI and 68 into engagement with their associated switchcontacts TI and I respectively. When the switch blade 8i engages switchcontact II and opens the switch contact 69 the ignition circuit totransformer I is deenergized as the energizing circuit for thetransformer I5 was completed through switch blade 67 and switch contact89, and the main control valve I2 will be energized by switch blade 8iengaging switch contact II. This energizing circuit may be traced fromthe input power line 88 through conductors 8'5, 85 and 89,'switch blade32, switch contact 34, conductors 90 and 9|, switch blade 61, switchcontact ii, conductor I09, main control valve i2, and conductors lit and94 back to the other input power line 80. The system is now operatingnormaily with pilot valve 20 energized and the main control valve I2energized.

As soon as the burner I0 has operated for a sufficient length of timethe thermostat 2| will no longer indicate a need for operation of theburner so that the switch blade 23 will be moved out of engagement withthe associated switch contact 24 by bimetal 22. This will open theenergizing circuit to the control relay I20 so that the switch blade I22will move from engagement with contact I24 into engagementwith contactI23. When blade I22 moves from engagement with contact I24, theenergizing circuit to the main control tube 25 is openedand the relay 29will become deenergized. When the blade I22 engages contact I23, thecontrol electrode 21 of device 25 is connected to the cathode 28 by acircuit that may be traced from control electrode 21, through conductorI30, switch contact I23, switch blade I22 and conductor I25 to cathode28. This circuit is provided to insure that the control electrode willbe at the same potential as the cathode upon a subsequent demand forburner operation, as indicated by the reoperation of the thermostat 2|.

When relay 29 becomes deenergized, the switch blades 3| and 32 will moveto their deenergized positions so that the switch blade 32 will be nolonger engaging switch contact 34 and the energizing circuit to thepilot valve 20 and the main control valve I2 will be broken and the fuelsupply to the burner I0 will be discontinued. With fuel no longersupplied to the pilot nozzle I8 there will be no flame emitting from thenozzle to intersect the flame electrode I5. With no rectifying actiontaking place in the flame electrode circuit the condenser 58 will not becharged to bias the triode 50 to be nonconducting. With triode 50conducting its energizing circuit may be traced from the secondary 41 attap 48 through conductors I02 and I03, resistor 63, conductors I04 andI05, anode 5|, cathode 53, and conductors I00 and I0! back to the lowerterminal of the secondary 41. It will be noted that the last tracedcircuit includes the resistor 63 which will have a voltage drop acrossit on the conducting half cycle of the triode 50 such that the upperterminal will be negative. This voltage drop is utilized to maintain thetriode 54 to be efiectively nonconducting when the triode 50 isconducting, since the triode 54 is phased to be conducting on the samehalf cycle as the triode 50. With both relays 29 and deenergized thecontrol apparatus is in a condition for a further operating cycle.

Operation of Figure 1 on flame failure In the operation discussed so farno consideration has been given to the safety features of the controlapparatus. One such feature provides for automatic shutdown in the eventthat there is a failure of the electrode I5 to detect the presence offlame. Assume that there is a need for operation of the burner and thethermostat 2| is closed so that the switch blade 23 engages switchcontact 24 which action completes the energizing circuit to relay I20and thereby to triode 25. With triode 25 energized the relay 29 willbecome energized so that the switch blades 3| and 32 will move intoengagement with their associated switch contacts 35 and 34 respectively.

As explained above, when switch blade 32 engages switch contact 34 onthe starting portion of the operating cycle the ignition transformer I5is energized as well as the pilot valve 20. Normally fuel would emitfrom the burner nozzle I8 and the ignition electrodes I3 and I4 wouldignite the same. In the event that there was no ignition of the fuelcoming from pilot nozzle I8 there would be no flame intersecting theflame electrode I5 and there would be no rectification in the flamedetection circuit to charge the condenser 58. With no charge on thecondenser 58 the triode 50 will be biased in its conducting range sothat there will be a current flow through the resistor 63 whichwilleffectively bias the triode 54 to be .nonconclucting so that it will notenergize the relay .65.

As noted above, the voltage drop across the resistor 63 is such that itsupper terminal is negative and its lower terminal is positive. Thisvoltage drop is utilized in the biasing circuit for the .main controltriode .25 .by reason of its connectionto the biasing condenser 39.Inasmuch as it is desired to bias the main control triode 25 below thepoint necessary to maintain the relay 2'9 energized when there is noflame present in the burner it or the pilot nozzle I8 a biasing circuitmust be established between the resistor 63 and. the biasing condenser39. This circuit may be traced .from the upper terminal of the condenser39 through conductor III, resistor 42, conductors H2 and we, resistor63, conductors I03, 3, and I26, switch contact I24, switch blade I22,and conductor I25 back to the lower terminal of the condenser 39. Itwill be noted that this last traced charging circuit for the condenser39 includes a resistor 42. The function of this resistor is to .delaythe charging time of the condenser '39 a predetermined amount. If thecondenser 39 is charged sufficiently negative by the voltageacross theresistor 63 the control electrode 2'! will bias the main control tube 25below the point necessary to maintain the relay 29 energized and thecontrol system will be rendered inoperative. To put the apparatus backin operation it is necessary to depress the manual 'reset lever 40 sothat it engages switch contact 4!. This will effectively short circuitthe condenser 39 so that it will discharge 'and'the main control tube 25will once again become conductive to reenergize the relay 29 and attemptto start the burner in operation again.

charged sufficiently negative to cut the tube off or a flame isestablishedat the burner.

The flame failure considered so far has been only in connection with thestarting cycle. If flame is established prior to the time that thecondenser 39 becomes fully charged, the condenser will be effectivelyshorted out and the control electrode 2'! and cathode28 of the maincontrol tube 2 will beconnected directly together so that the controltube will remain conductive. This shunting circuit will occur only whenboth the main control relay 2% and the flame detection relay B5 areenergized so that the switch blade 3! of relay 29 engages switch contact35 and the switch blade 68 of relay 65 engages switch contact 13. Withthese two relays energized, a circuit may be traced from the controlelectrode 21 through conductors II! and H5, switch blade 68, switchcontact 13, conductor I I 6, switch blade 3|, switch contact 35, andconductor H3 back to the oathode 23. This circuit is actually a shortcircuit connection which connects the control electrode 21 to thecathode 28 and with such a connection triode 25 will continue to conductand maintain relay'29 energized.

Should the apparatus be operating normally so that thereis fuel beingsuppliedto both .the

pilot nozzle l8 and the burner I0 and there is a subsequent flamefailure, the flame detection relay 65 will become deenergized. With therelay becoming deenergized the switch blad 51 will engage switch contact69 so that the energizing circuit to the ignition transformer I5 willonce again be completed. The energizing circuit to the main controlvalve I2 will be broken by the movement of the switch blade 61 out ofengagement with its associated switch contact II and the shuntingcircuit for condenser 39, associated with the input of control tube 25,will be opened by the movement of the switch blade 68 out of engagementwith its associated switch contact Ill. In the event that thereenergization of the ignition transformer I5 fails to establishcombustion at the pilot nozzle I8 within a predetermined time thecondenser 39 will be charged sufficiently through resistor 32 to biasthe triode 25 below the point necessary to maintain relay 29 energizedand when this occurs the switch blades 3i and 32 will move out ofengagement with their associated contacts 35 and 34 respectively so thatthe pilot valve 23 and the ignition transformer I5 will be deenergizedand the system will be inoperative until such time as the manual resetlever at is pushed into engagement with switch contact GI to once againdischarge the condenser 33. With condenser 39 discharged by the resetlever actuation the control tube will once again become conductive andattempt to initiate operation of the burner andif combustion fails totake place the condenser 39 will once again be charged to a point whereit will bias the control tube 25 to be effectively nonconducting.

Operation of Figure 1 on ground out As it ispossible to have .acondition where the flame electrode 55 will be short-circuited with thepilot nozzle I8, which condition is referred to as a ground outcondition, it is desirable to see that the control apparatus does notbecome operative. With the electrode l5 shorted to the pilot nozzle i8there can be no rectification of the flame detection circuit andtherefore the condenser 58 will not be charged so that it will have nobiasing effect on the triode 55 which will remain conductivesufficiently to maintain the triode 54 nonconductive as explained above.With the triode 54 effectively nonconductive, the relay will not becomeenergized so that the shunting circuit around the condenser 39 will notbe completed and the condenser 39 will be charged by the voltageexisting across resistor .63, as explained above, to bias the maincontrol tube 25 below the point necessary to maintain relay 29energized; When relay 29 becomes deenergized both the ignitiontransformer 65 and the pilot valve 20 will become deenergized and thesystem will remain inoperative until such time as the manual reset leveris depressed to discharge the condenser 39.

Operation of Figure 1 upon false indication of flame As the controlapparatus employs an electronic flame detector, it is desirable toemploy some means of preventing operation of the control apparatus whenthat flame detector is falsely indicating flame as might occur shouldsome of the elements within the triodes 50 or 54 become shorted or opencircuited in such a manner that the triode 54 remains conductive and therelay 65 energized. This is accomplished in the present invention byapplying an alternating current bias voltage to the control electrode 21of the main control tube 25 whenever the relay 95 is energized and thereis no demand for operation of the burner or when the relay 29 isdeenergized. When the relay 29 is deenergized so that the switch blade3I engages switch contact 33 and when the relay 55 is energized falselyindicating the presence of flame so that the switch blade 68 is engagingswitch contact 10 it is possible to complete the biasing circuit to thecontrol electrode 21 of the main control tube 25. This circuit may betraced from the tap 49 of the secondary 41 through conductor II9, switchcontact 33, switch blade 3I, conductor I I6, switch contact 10, switchblade 68, and conductors H and III to the control electrode 21. Toestablish a common potential between the biasing voltage on the controlelectrode 21 and the voltage on the oathode 28 it is necessary to havethe cathode 28 effectively connected to a point on the transformersecondary 41. This is done by direct connection of the cathode 28through conductor I25, switch blade I22, switch contact I24, andconductors 82, H3, and I02 to the tap 48 of the secondary 41. It will benoted that this last traced circuit is completed only when thethermostat 2I is closed to energize the relay I20 upon a demand for moreheat but since the control relay 29 is deenergized when the thermostatis open it will make no differenoe since the relay will not becomeenergized due to the completion of the last traced biasing circuit. Thevoltage between the taps 49 and 48 of the secondary 41 are of such phasewith respect to the alternating current voltage on the triode 25 thatthe control electrode 21 will be negative with respect to the cathode 28on the normally conducting half cycle of the triode 25. This voltagewill remain biasing the control electrode 21 until the' fault has beenremoved from the flame detection portion of the control apparatus. Withtriode 25 so biased, the current flow through the triode will not besufficient to energize relay 29. It will be impossible to appreciablyaffect this biasing voltage by depressing the reset lever 43 because ofthe fact that the resistor 42 is tapped at 43 and there is suflicientresistance in the circuit shunting the control electrode 21 of thecathode 28 when the lever is depressed that the alternating currentbiasing voltage will not be short-circuited to permit en- 0 ergizationof the main control relay 29.

As soon as the fault has been cleared from the flame detection portionof the control apparatus the relay 65 will become deenergized so thatthe switch blade 68 will move out of engagement with its associatedswitch contact and the alternating current biasing circuit will beinterrupted to thereby permit operation of the control apparatus in thenormal manner.

Figure 2 The apparatus shown in Figure 2 accomplishes the same type ofcontrol as that of the apparatus shown in Figure 1. In Figure 2, thecomponents Which correspond to those of Figure 1 carry the samereference numerals. The circuits in Figure 2 have been slightly modifiedin the timing circuit and in the component checking circuit.

In Figure 2, the room thermostat 2I is effective to control appropriateelectrical circuits within the housing I31, the latter of which initiateand check the operation of the pilot burner I8 and the main burner I0.Located within the housing I31 is a flame detection circuit whichcorresponds identically to that of Figure 1 except that a modifled relayI65 has been added in the output circuit of the discharge device 54.This relay comprises a relay winding I65, a plurality of switch bladesI61, I60, I69 and I10. The switch blade I61 is normally biased by meansnot shown into engagement with an associated switch contact I12. Whenthe relay is energized the switch blade moves into engagement with acontact I1I. Switch blade I68 is normally biased out of engagement withan associated contact I13 and switch blade I69 is normally biased out ofengagement with a contact I14. Switch blade I10 is normally biased intoengagement with a contact I15. Supplying power to the flame detectioncircuit is a transformer I45 having a primary winding I46 and a pair ofsecondary windings I41 and I48. The secondary winding I41 is tapped atI49. The secondary I48 is used to supply the filament voltages for thedischarge devices of the flame detector and for the main control tube25. This transformer is also used for alternating current biasingpurposes in a manner which will be understood when the operation of thepresent figure is considered.

The operation of the flame detector shown in Figure 2 is the same asthat of the flame detector shown in Figure 1 and the output controlrelay I65 will be energized when a flame is detected and will bedeenergized when there is no flame or there is faulty operation at theflame rod 15.

A control relay I29 has been added to the output circuit of the maincontrol tube 25 and this relay comprises a relay winding I30, and aplurality of switch blades I3I, I32 and 233. The switch blades arenormally biased out of engagement with associated contacts I34, I35 andI36 and the blade I32 is biased into engagement within associatedcontact I31.

An additional control relay I50 is associated with the timing circuit onthe input of the main control tube 25. This control relay comprises arelay winding I5I, a plurality of switch blades I52, I53 and I54 whichare normally biased out of engagement with their associated switchcontacts I55, I58 and I51. Associated with the relay I50 is a currentlimiting resistor I60.

Associated with the input of the main control tube 25 is a timingcondenser I6I, a timing resistor I62 and a grid lead resistor I63. Apair of filament heaters I64 are connected to the sec ondary winding I48and are utilized for heating the cathodes of triodes 25, 50, and 54.

Operation of Figure 2 In considering the operation of Figure 2, it willbe noted that the apparatus as shown upon the drawing is in thedeenergized position with the room thermostat not calling for burneroperation and the control relays all deenergized. Also deenergized arethe ignition device, the pilot valve and the main valve. When there is aneed for burner operation the room thermostat 2I will close and willcomplete an energizing circuit to the main control tube 25. Thisenergizing circuit may be traced from. the lower terminal of secondaryI41 through conductors I and I8I, relay winding I30, conductor I82,anode 26, cathode 28, conductors I83, 226 and I84, bimetal 22, switchblade 23, switch contact 24, and conductors I and I88 to tap I49 onsecondary I41. With this last traced energizing circuit complete, thecurrent flow therethrough will be sufficient to energize the control l11 relay I23 so that the switch blades I3 I, I32 and I 33 will moveintoengagement with their associated contacts I33, I33 and I33,respectively.

When switch blade I 33 engages contact I36, an energizing circuit iscompleted through the ignition transformer I5 and the pilot valve 23.This energizing circuit may be traced from the input power line 33through conductors I33, I9I, and H12, switch contact I36, switch bladeI33, conductor I93, switch contact I15, switch blade I'Ill, conductorI34, primary I5 of ignition transformer I5, andconductors I35. and I96back to the other input power line 88,

The energizing circuit for the pilot valve 23 is almost identical to theabove traced circuit except that the circuit does not include anycontacts of the flame indicating relay I35. This circuit may be tracedfrom the upper input power line 80 through conductors I93, ISI and I32,switch contact I33, switch blade I33, conductors I33 and I91, pilotvalve 23, and conductors I35 and [-33 to'the. lower input power line 88.

Also energized, upon the energization of the control relay I23 is thecontrol relay I53. The energizing circuit for this relay may be tracedfrom the input power line 8i! through conductors I90 and I9I', switchcontact I34, switch blade I3 I, conductors 200, switch contact I12,switch blade I61, conductor 2I1I, conductor 2E3, relay winding I5 I andconductors 234 and 235 to the other input power line 83. When relay I38becomes energized a holding circuit therefor is completed which isindependent of the relay contacts of either relays I29 and I35 and thisholding circuit may be traced from the input power line 33 throughconductors I93 and 2&2, switch blade I52, switch contact I55, resistorI53, conductor 233, relay winding I5I, and conductors 2G4 and 235 to theother input power line 38. The further circuit. completed by theenergization of the relay I5!) is a charging circuit for the timingcondenser IBI. It will be recalled that in considering the operation ofthe flame indicator in Figure 1, there was a voltage drop across theload resistor 63. such that the upper terminal of the resistor wasnegative and the lower terminal was positive when the triode 5!! is onthe conducting half cycle of the power supply. With a condenser E lconnected in parallel with the resistor I53, the polarity across theresistor I53 will then be maintained there by the fact that on the halfcycles in which the tube 53 is not conducting, the condenser 64 will bedischarging through the re sistor 63 and will be maintaining thepolarity thereon. This charging circuit may be traced from the lowerterminal of resistor 63 through conductors 2H} and I 35, switch contact25, switch blade 23', bimetal 22, conductor I34, condenser IBI,conductor 2, switch contact I56, switch blade I53, conductor 2 I2,switch blade I53, switch contact I51, timing resistor I 62, andconductor 2I3 back to the upper terminal of resistor 33. This chargingcircuit, when completed, will start charging the timing condenser I6! sothat its upperterminal will be negative with respect to its lowerterminal.

If a flame is established at the pilot nozzle I3, the presence of thepilot flame will be detected by the flame rod assembly and will beindicated by the operation of the relay I63. When this flame, indicatingrelay becomes energized the switch blades I61, I38, I69 and I19 will allmove to the energized position where the blade I31 will engage switchcontact I1I, blade I68 will engage contact I13 and blade I69'wil1 engagecontact I 14. The blade I10 will move'out. of. engagement with contactI15. When blade I'GS engages contact I14 the control electrode 21 isconnected" directly to the cathode 28 of the main control tube 25 sothat any charge upon the timing condenser I6I will have no efiect uponthe operation of the control tube. This shorting circuit may be tracedfrom the control electrode 21' through conductors 2I5 and 2I6, switchblade I63, switch contact I14, conductor 2I1, switch blade I32, switchcontact I35, conductor 2I8 to cathode 28. With this shorting circuitcomplete, the control tube will stay conducting and will maintain thecontrol relay I29energized.

When the flame indicating relay I65 becomes energized the energizingcircuit to the ignition transformer I5 is broken by the movement ofswitch blade I 13 out of engagement with its contact I15. Inasmuch asthepilot valve is energized independently of this last switch contact,the pilot valve will remain energized. When the switch blade I63 engagescontact I13, an energizing circult-is completed tothe main valve I 2 andthis energizing circuit may be traced from the input power line 83through conductors I93, I9I and [32, switch contact I36, switch bladeI33, conductors I 93 and 2223, switch contact I13, switch blade I38,conductor 222, main valve I2, and conductors 223 and I93 back to theother input power line 83. When the switch blade I61 engages contactill, a short circuit is completed across the relay winding I 5i so thatthe relay I50 willbecome deenergized. This shorting circuit may betraced from the input power line 88 through conductors 263 and 225,switch contact I1 I, switch blade I61, conductor 23!, conductor 233,relay winding I5I and conductor 234. back to conductor 205. When relayI53 becomes deenergized, the switch blades: will move out of engagementwith their associated contacts and the charging circuit for the timingcondenser ISI will be opened and the holding circuit for the. relayitself will be opened.

The apparatus is now operating normally with the main control. relay I23energized, the flame indicating relay I35 energized and the controlrelay I53 deenergized. Further, the ignition transformer is deenergizedand the main pilot valve and main valve are energized.

As soon as the thermostat 2I no longer indicates the need for burneroperation, the switch blade I23 will move out of engagement with contact24 and this will open the energizing circuit to the main control tube25. With the control tube 25 deenergized, the main control relay I29will become deenergized. When the control relay I 29 becomes deenergizedthe switch blade I33 will move out of engagement with contact I36 toopen the energizing circuit through the main valve I2 and the pilotvalve ZIlso that the burner assembly will be shut down. When flame is nolonger detected by the flame rod 15, the flame indicating relay I65 willbecome deenergized. When this occurs, the apparatus will be completelyshut down and will be ready for another operating cycle upon a furtherdemandfor burner operation as indicated by the operation of the roomthermostat 2I l Operation of Figure 2 on flame failure If the operatingcycle is started in a normal manner by the room thermostat first closingto indicate a need for burner operation, the control relay I 29 and thecontrol relay I53 will become energized, in the manner described above.When the relay I29 becomes energized the pilot valve 20 and the ignitiontransformer I will be energized to attempt to establish a flame at thepilot nozzle I8. When the relay I50 becomes energized the chargingcircuit to the timing condenser IEI is completed from the load resistor63. If no flame is detected by the flame rod I5, the flame indicatingrelay I65 will remain in the deenergized position and the chargingcircuit to condenser I6I will not be interrupted. This will mean thatafter a predetermined time, a time dependent upon the size of the timingresistor I62 and the timing condenser IBI, the condenser IBI will assumea charge which is negative on the upper terminal and positive on thelower terminal and of sufficient magnitude to bias the main control tube25 below the conducting point necessary to maintain the control relayI29 energized. When the relay I29 becomes deenergized the ignitiontransformer and the pilot valve will be deenergized. Inasmuch as thecontrol relay I52 establishes a holding circuit for itself, independentof any contact with either relay I29 or IE5, this relay will remainenergized and when so energized the charging circuit to the timingcondenser IGI will remain intact and will maintain the bias on thecontrol group 25 below the point necessary to pull in the control relayI29. The apparatus will stay in this condition until such time as thereset button is actuated so that the switch blade 40 moves intoengagement with contact 4|. When this occurs, the condenser I6I will beshorted out by a circuit that may be traced from the upper terminal ofcondenser IGI through conductor 2| I, switch contact I55, switch bladeI53, conductor 2I2, switch blade I54, switch contact I51, switch contactII, switch blade 40, and conductor 226 to the lower terminal ofcondenser IBI.

When the condenser Itl has been discharged, it is possible to reenergizethe main control relay I29 since the control electrode 21 will have thesame potential as the cathode 28 and the current flow through relay 25should be suincient to energize the main control relay I29. This willmean that a further attempt will be made to establish flame at the pilotnozzle I8. If flame is established, the operation of the apparatus willbe as explained above, and the flame will be indicated by the operationof the flame indicating relay I65 which in turn will energize the mainvalve I2 so that the apparatus will be operating normally.

In the event that the apparatus should be operating normally and thereshould be a subsequent flame failure so that the flame indicating relayI65 became deenergized, it is also desired that the apparatus berendered inoperative and the control valve be deenergized. It will benoted that as soon as the flame indicating relay I85 becomesdeenergized, with the room therstat 2| still calling for operation ofthe burner, the short circuit around the relay winding I5I will beremoved and the relay will become energized. When the relay does becomeenergized the charging circuit for the timing condenser IBI is completedand, after a predetermined time, the condenser will charge and will biasthe control tube 25 to a point where its conductivity will no longermaintain the control relay I29 energized. When the relay I29 becomesdeenergized the energizing circuit to the main valve and pilot valvewill be deenergized and the burner apparatus will be completely shutdown. In order to put the apparatus back in operation it is necessarythat the reset switch 40 be actuated to discharge the timing condenserIGI and when this occurs, a further attempt will be made to establishburner operation and if this fails, the apparatus will again be shutdown.

Operation of Figure 2 upon false indication of flame In the event thatthere is a false indication of flame as would occur if the flameindicating relay I55 were to remain in the energized position after theburner has been shut down by the opening of the room thermostat 2I, itis desired that there be no further operation of the control apparatusuntil the fault causing operation of the flame indicating relay isremoved. The maintaining of the apparatus inoperative is accomplished insomewhat the same manner as was accomplished in the apparatus shown inFigure 1. In the present figure, when there is a false indication offlame, an alternating current bias is obtained from the secondarywinding supplying energizing voltages for the filaments I54. Thisalternating bias from filament secondary I48 is applied between thecontrol electrode 21 and cathode 28. The circuit from the secondary I48may be traced from the upper terminal of the secondary through conductor23E, switch contact I31, switch blade I32, conductor 2I'I, contact I'M,switch blade I59, and conductors 2 I 8 and M5 to the control electrode2?. The connection of the secondary I48 to the cathode may be tracedfrom the lower terminal of secondary I48 to conductor 23I, conductorI85, conductor I85, switch contact 24, switch blade 23, and conductorsI84, 225 and I83 to cathode 28. It will be noted that this last tracedcircuit is completed only upon the closing of the room thermostat 2 I.This will be of no significance inasmuch as soon as the biasing circuitis completed, a negatively phased alternating current bias is suppliedbetween the control electrode 21, cathode 28, such that the controlelectrode 21 will be negative with respect to the cathode 28 on the halfcycle when the anode 26 is positive with respect to the oathode, or onthe normally conducting half cycles. With the control electrode biasednegatively with respect to the cathode on the conducting half cycle ofthe tube, the current flow will not be suflicient to energize thecontrol relay 29 and the apparatus will stay in a shutdown positionuntil the fault causing fake operation of the relay IE5 is removed. Asin Figure l, the depressing of the reset switch will have no effect uponthe operation upon a component failure. This will be understood when itis noted that the relay I50 will be deenergized with relay I65 operatingdue to the short circuit around the relay. With relay I50 deenergized,it is impossible to complete a shorting circuit between the cathode 28and control electrode 2'! by the depressing of the reset switch 40.

Conclusion From the foregoing it can be seen that I have provided aburner control apparatus which is operative to shut the burner down upona flame failure, to provide against ground out conditions of the flamedetection circuit, and to maintain the control apparatus inoperativewhen there is a false indication of flame by the flame detection relay.Further it may be seen that I have provided a control apparatus whichemploys condenser timing for establishing the safety shutdown of thecontrol apparatus and provi ing with that feature a fail safe circuitwhich can be rendered ineffective upon a flame failure orcanbemaintained eifective continuously upon a false. indicationof flame.

Although I have described my invention in connection with a gas burnercontrol, and while it is particularly well adapted for use there, itwill be obvious to those skilled in the art that my invention could beapplied to any burner control apparatus where it is desired to use anelectron discharge device and a condenser timed input safety biasingcircuit. Therefore, I intend to be limited solely by the scope of theappended claims in which I claim:

1. Apparatus for controlling a fuel burner having a control means forindicating the need for burner operation comprising in combination, anelectron. discharge device adapted to be energized by the control means,relay means, said relay means having switch. contacts adapted toenergize means for initiating operation of the burner, means connectingsaid relay means in the energizing circuit of said discharge device,biasing means, a source of biasing potential, time delay means, meansconnecting said biasing means, said time delay means and said source ofbiasing potential in biasing relation to said discharge device so thatsaid discharge device will be rendered inoperative after a predeterminedtime delay, electric switching means adapted to be actuated by meansindicating proper burner operation, means including said electricswitching means for rendering said biasing means ineffective when saidelectric switching means is actuated and indicating the presence ofcombustion, additional biasing means, and means including said electricswitching means connecting said additional biasing means to said discharge device when said electric switching means is in actuated positionand indicating the presence of combustion and there is no demand foroperation of the burner to maintain said discharge device inoperativeupon a subsequent demand for burner operation.

2. Apparatus for controlling a fuel burner having a control means forindicating the need for burner operation, comprising in combina tion, anelectron discharge device having input and output terminals, a source ofpower, an electric circuit adapted to be completed by the control meansfor connecting said discharge device to said source of power, a relay,means connecting said relay to the output terminals of said dischargedevice so that said relay is energized when the current flow in saiddischarge device is greater than a predetermined value, means actuatedby said relay for initiating operation of a burner when said relay isenergized, a condenser, means connecting said condenser in biasingrelation to the input terminals of said discharge device, a chargingcircuit connected to said condenser by means including the control meansfor charging said condenser after a predetermined time delay to apotential which will bias said. discharge device below the pointnecessary to maintain said relay energized, electric means adapted to beenergized by means indicating proper burner operation, switch meansactuated by said electric means for rendering inoperative said chargingcircuit so that said discharge device vwill remain operative, a out 01fcircuit including said source of power, means connecting said cut offcircuit to said discharge device, and further switch means actuated bysaid electric means for completing said out off circuit only when. saidrelay is deenergized and said switch means is in actuated position sothat said discharge device will be maintained inoperative upon asubsequent demand for. burner operation by the control means.

3. In a control system for a fuel burner. having a control meansassociated therewith for in.-- dicating, the need for burner operation,in combination, an electron discharge device adapted to be energized bythe. control means, a relay having switch contacts for initiatingoperation of the burner, means connecting said relay in. circuit withsaid. discharge device, a condenser, means connecting said condenser incurrent. controlling relation to said discharge device, a chargingcircuit connected to said condenser, said charging circuit beingoperable to. charge said condenser after a predetermined time delayfollowing the. operation of the control means. so. that said. condenserwill. reduce the. current. flow in said. discharge device below thepoint necessary to maintain said. relay energized, electrically operablemeans having switch contacts. and. adapted to be energized by combustionresponsive means, means including switch contacts actuated by saidelectrically operable means for rendering said charging circuitineffective, biasing means, circuit means connecting. said biasing.means to. said. discharge device, and means including switch contacts ofsaid electrically op-- erable means and switch contacts of said relayfor completing an electrical circuit from said biasing means to saiddischarge device to maintain said device inoperative when there has beenno need for operation of the burner and saidcombustion responsive meansis indicating the presence of combustion and the control meanssubsequently indicates a need for burner operation.

4. Apparatus for controlling a fuel burner system having a fuel burnerand a control means for indicating the need for operation. of theburner, comprising in combination, a source of power, an electrondischarge device, a relay, an electric circuit adapted to be completedby the control means for connecting said discharge device and said relayin an energizing circuit to said source of power, means actuated by saidrelay when energized for initiating operation of the burner, electricmeans adapted to be energized by combustion responsive means, first andsecond biasing circuit means, means including said electric means andsaid relay for connecting said first biasing circuit means in currentcontrolling relation to said discharge device to render said deviceinoperative after a predetermined length. of time when only said relayis operative, and means including said second biasing circuit means tomaintain said device inoperative when said combustion responsive deviceis falsely indicating the presence of flame following a normal burnershutdown and the control means is subsequently actuated.

5. A control apparatus for a fuel burner system having a fuel burner anda control means for indicating the need for burner operation, comprisingin combination, a source of power, an electron discharge device, a relayhaving in and out switch contacts, an electric circuit connecting saiddischarge device and said relay in an energizing circuit when saidcircuit is completed by means including the control means, meansactuated by certain of the in contacts of said relay for initiatingoperation of the burner, combustion responsive means having in switchcontacts actuated when a burner flame is present, first and secondbiasing means, first circuit means including the control means forconnecting said first biasing means to said discharge device in currentcontrolling relation to render said device inoperative after apredetermined length of time, second circuit means including in contactsof said relay and said combustion responsive means for rendering saidfirst biasing means inefiective when a burner fiame is present, thirdcircuit means including in contacts of said combustion responsive meansand out contacts of said relay connecting said second biasing means tosaid discharge device to maintain said device inoperative when saidcombustion responsive means is operating falsely and there is asubsequent indication of a need for burner operation by the controlmeans.

6. Control apparatus for a fuel burner system having a fuel burner and acontrol means for indicating the need for burner operation, comprisingin combination, first and second electron discharge devices, first andsecond relays having a plurality of switch contacts, a source of power,a first electric circuit including said control means for connectingsaid first relay and said first discharge device to said source ofpower, switch means actuated by said first relay for initiatingoperation of the burner, a second electric circuit connecting saidsecond relay and said second discharge device to said source of power, aburner flame responsive circuit, means connecting said circuit incurrent controlling relation to said second discharge device so thatsaid discharge device will render operative said second relay on thepresence of flame, first and second biasing means, circuit meansconnecting said first biasing means to said first discharge device whensaid first circuit is completed so that after a predetermined length oftime said first discharge device will be rendered inoperative, a thirdelectric circuit including switch means actuated by said first andsecond relays for short circuiting said first biasing means, and afourth electric circuit including switch means actuated by said secondrelay connecting said second biasing means to said first dischargedevice to maintain said first discharge device inoperative when saidflame responsive circuit is falsely maintaining said second dischargedevice operative and there is a subsequent indication of a need forburner operation by the control means.

7. Control apparatus for a fuel burner system having a fuel burner and acontrol means for indicating the need for burner operation, comprisingin combination, an electron discharge device having an anode, cathodeand control electrode, an alternating current source of power, a relay,a first electric circuit for connecting said relay and the anode-cathodecircuit of said discharge device to said source of power so that saiddevice is conductive on alternate half cycles of said source of power,switch means actuated by said relay for initiating operation of theburner, a condenser, means connecting said condenser between the controlelectrode and cathode of said discharge device, a source of chargingcurrent, time delay resistive means, a second electric circuitconnecting said source of charging current through said time delayresistive means to said condenser so that said condenser is slowlycharged to bias said discharge device below the point necessary tomaintain said relay energized, combustion responsive means actuated onthe presence of flame, means including said combustion responsive meanswhen actuated for discharging said condenser to maintain said dischargedevice operative, a third electric circuit for effectively connectingsaid source of power to the control electrode of said discharge deviceonly when said combustion responsive device is actuated and said relayis deenergized, said third circuit having an alternating current phaseopposite the phase of said first circuit,

8. In a safety control system for apparatus normally operable whenenergized to establish a predetermined condition, in combination, meansincluding an electron discharge device having an input circuit andcontrollin said apparatus so that said apparatus is energized only whensaid discharge device is conductive, first means responsive to acondition indicative of the need for conduction of said device foroperating said controlling means, means including a condenser in theinput circuit of said device for controlling the conductivity of saiddevice to cause the current flow to maintain a predetermined level for apredetermined time following a call for operation by said firstresponsive means, second means independent of said controlling meansresponsive to the establishment of said predetermined condition forshunting said condenser so as to maintain said discharge deviceconductive, and biasing means connected to said device for maintainingsaid device nonconducting when said first responsive means becomesoperative indicating the need for operation of said control means andsaid second means is operating falsely.

9. Control apparatus for a fuel burner system having a fuel burner and acondition responsive means for indicating the need for burner operation,comprising in combination, means for initiating operation of the burner,control means for said initiating means including an electron dischargedevice having an input circuit and an output circuit, said control meansbeing effective to operate said operation initiating means only whensaid discharge device is conductive, and means for controlling theconductivity of said discharge device, said last named means comprisingsaid condition responsive means operable to complete an energizingcircuit for said discharge device upon the need for operation of aburner, a first biasing circuit which is operable to deenergize saiddischarge device after a predetermined time when the burner fails tooperate, a combustion responsive means which is operable to shunt outsaid first biasing circuit when said combustion responsive means andsaid responsive means are operative, and a second biasing circuitincludin said combustion responsive device connected to the input ofsaid discharge device to maintain said discharge device inoperative onlywhen said combustion responsive means is operating falsely and there isa subsequent demand for burner operation by the condition responsivemeans.

10. Control apparatus having means for controlling a fuel burner toestablish combustion, comprising in combination, means including anormally conducting electron discharge device having a control electrodefor initiating operation of the burner controlling means when saiddischarge device is conductive, and regulating means for controlling theconductivity of said discharge device, said regulating means includingswitch means for completing the conductive circuit of said dischargedevice upon need for operation of said burner controlling means toestablish combustion, means responsive to establishment of combustionfor maintaining said discharge device conductive when said apparatus isfunctioning properly, biasing means, and means including said conductivewhen combustion responsive means connecting said biasing :means to thecontrol electrode of said discharge device for maintaining said devicenonsaid combustion responsive means indicates establishment ofcombustion and when said switch means are not indicatin need foroperation of said burner controlling mean to establish combustion.

:nection, means including combustion responsive means for maintainingsaid relay means operative upon the establishment of combustion, abiasing voltage, and means including said combustion responsive meansfor connecting said biasing voltage to said control electrode to apply avoltage thereto and prevent operation of said discharge device when saidcombustion responsive .means is falsely indicating the presence ofcombustion.

12. Control apparatus for a fuel burner, comprising in combination, anelectron discharge device having an anode, a cathode and controlelectrode, a source of power, means connecting said source of power inenergizing relation to said anode and said cathode, relay meansconnected in said last named connection adapted when energized toinitiate operation of the burner, a condenser timing circuit, meansconnecting said timing circuit in current fiow controlling relationshipto said discharge device, combustion responsive means for indicatingproper operation of the burner, said combustion responsive meanscomprising a source of signal potential which is indicative of thepresence or absence of combustion, means connecting said combustionresponsive means to said timing circuit so that upon failure of saidcombustion responsive means to indicate the presence of combustion saidtiming circuit will be charged after a predetermined time delay by saidsignal potential to render said discharge device nonconductive and saidrelay means deenergized, and further means including said combustionresponsive means for shunting said timing circuit when there is a flameat the burner.

13. Control apparatus for a fuel burner having control means forindicating the need for operation of the burner, the combinationcomprising, a source of power, an electron discharge device having aninput and output circuit, a, first control relay for initiating burneroperation, means connecting said relay in the output circuit of saiddevice, circuit means adapted to be completed by the control means forconnecting said device in an energizing circuit to said source of power,biasing means, a timing condenser, a second control relay, meansincluding said first relay when energized for connecting said secondrelay to said source, means including said second relay for connectingsaid biasing means to said icondenser, means connecting said condenserto said input of said device for rendering said device inoperative aftera predetermined time following the energization of the second relay, andfurther means for rendering said biasing means ineffective to chargesaid condenser when there is an indication of burner flame.

14. Control apparatus for a fuel burner having control means forindicating the needfor operation of the burner, the combinationcomprising,

a source of power, an electrondischarge device having an input andoutput circuit, a first control relay for initiating burner operation,means connecting said relay in the output circuit of said device, meansadapted to be'energized by the control means for connecting said devicein an energizing circuit to said source of power, biasing means, atiming condenser, a second control relay, means including said firstrelay when energized for connecting said second relay to said source,means including said second relay for connecting said biasing means tosaid condenser, means connecting said condenser to said input of saiddevice for rendering said device inoperative after a predetermined timefollowing the energization of said second relay, and further means forrendering said biasing means ineffective to charge said condenser whenthere is an indication of burner flame and to render inoperative saidsecond relay means.

15. Control apparatus for a fuel burner having control means forindicating the need for burner operation, the combination comprising, asource of power, an electron discharge device, a control relay forinitiating burner operation connectedin circuit with said device, meansadapted to be energized by the control means for connecting said deviceand said relay in an energizing circuit to said source, energizablemeans for indicating proper burner operation, first biasing circuitmeans including said burner operation indicating means for renderinginoperative said device after a predetermined time delay upon a failureof burner operation, a reset switch associated with said first biasingcircuit means for rendering said device and relay operative to attemptto initiate a further burner operation, and second biasing circuit meansfor rendering said device inoperative upon said indicating meansoperating falsely, said reset switch being ineffective to initiateoperation of said device when said indi cating means is operatingfalsely.

16. Control apparatus for a fuel burner having control means forindicating the need for operation of the burner, the combinationcomprising, a source of power, an electron discharge device having aninput and output circuit, a first control relay for initiating burneroperation, means connecting said relay in the output circuit of saiddevice, means adapted to be energized by the control means forconnecting said device in an energizing circuit to said source of power,biasing means, a timing condenser, a second control relay, meansincluding said first relay when energized for connecting said secondrelay to said source, means including said second relay for connectingsaid biasing means to said condenser, means connecting said condenser tosaid input of said device for rendering said de vice inoperative after apredetermined time following the energization of said second relay, areset switch for shunting said timing condenser to initiate operation ofsaid device following deenergization of said device by said timingcondenser, means responsive to proper burner operation for renderingsaid second relay inoperative and for shuntin said input, and meansincluding said second relay for rendering said reset switch ineifectivewhen said burner operation responsive means is operating falsely.

17. Control apparatus for a fuel burner having control means forindicating the need for operation of the burner, the combinationcomprising, a first electrical-switching means adapted to be energizedby thecontrol means, an electron discharge device, a source of power, asecond electrical switching means, means including said first switchingmeans when energized for connecting said device and said secondswitching means in an energizing circuit to said source, means actuatedby said second switchin means when energized for energizing the burner,a third electrical switching means adapted to be energized upon properoperation of the burner, first and second biasing circuit means, meansincluding said third switching means and said second switching means forconnecting said first biasing circuit means in current controllinrelation to said discharge device to render said device inoperativeaiter a predetermined length or time when onl said first and secondswitching means are operative and said third is inoperative, and meansincluding said second biasing circuit means to maintain said deviceinoperative when said third switchin means is falsely indicating properburner operation, said first switching means is energized and saidsecond switching means is deenergized.

18. Control apparatus for a fuel burner having control means forindicating the need for operation of the burner, the combinationcomprising, a first electrical switching means adapted to be energizedby the control means, an electron discharge device, a source of power, asecond electrical switching means, means including said first switchingmeans when energized for connecting said device and said secondswitching means in an energizing circuit to said source, means actuatedby said secon" switching means when energized for initiating burneroperation, a third electrical switching means adapted to be energizedupon pr per operation of the burner, biasing means, and means said thirdswitching means and said second switching means for connecting saidbiasing means in current controlling relation to said 0 scharge deviceto render said device inoperative after a predetermined time when onlysaid first and second switching means operative said third switchingmeans is inoperative, and means in cluding said first switching forrendering ineffective said biasing means when said first switching meansis rendered inoperative upon the energizing circuit therefor beingopened by the control means.

J OHN lvl. VIIIEON.

REFERENCES CETED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,170,497 Gille Aug. 22, 19392,243,071 Crago May 2'7, 1941 2,293,474 Schneider Aug. 18, 19422,368,893 Spangenberg et 'al. Feb. 6, 1945

